Normal human speech utilizes the flow of expired air from the lungs up through the trachea and the larynx to vibrate the vocal cords in the larynx. If disease or injury requires the removal of the larynx, it becomes necessary to provide an alternative sound producing apparatus as a substitute for the vocal cords. Since the larynx normally blocks the lungs from contamination by esophageal contents, the surgeon must block the passage between the trachea and the pharyngeal esophagus. Consequently, during a typical laryngectomy, the surgeon creates an opening, or stoma, at the base of the patients neck to which the trachea is permanently diverted.
In one method of facilitating speech by the laryngectomee, the surgeon creates a new path for air to travel from the lungs and trachea to the pharyngeal esophagus. A voice prosthesis in the form of a cylindrically shaped, one-way valve may be inserted into this tracheoesophageal passageway. Various efforts have been made to provide a tracheal valve that will remain open to accommodate normal breathing, will close under speaking pressure so that exhalation products will pass into the pharynx for speech, and will open under higher pressure. Included are the techniques and devices illustrated and described in U.S. Pat. Nos. 4,582,058; 7,025,784; and 7,370,654. The disclosures of these references are hereby incorporated herein by reference. This listing is not intended as a representation that a complete search of all relevant prior art has been conducted, or that no better references than those listed exist.
To permit speech without manual occlusion of the stoma, a flange can be fastened over the tracheostoma and a valve inserted into the flange. This arrangement diverts the air flow from the trachea through the voice prosthesis. It is known in the prior art to provide tracheostoma valves with a movable diaphragm biased to an open position, as described in, for example, U.S. Pat. Nos. 5,059,208 and 7,370,654. Normal breathing pressures are insufficient to move the diaphragm to a closed position. Hence, the patient may readily inhale and exhale past the diaphragm.
Speech pressures, however, are initiated at somewhat higher levels. These higher pressures move the diaphragm to a closed position, blocking the free discharge of air to the atmosphere. The exhaled air can thus be diverted through the voice prostheses to the oral cavity where it produces sound that can be shaped into speech.
With different patients and changing exertion and respiration levels, no single diaphragm has the correct mechanical characteristics to work ideally in all situations. In the past, it has been necessary for the doctor to select a compromise valve diaphragm that works best for an individual patient in an average state of exertion.